1. Field of the Invention
The present invention relates to circuit interrupters generally and, more specifically, to those kinds of circuit interrupters having a thermal tripping operation.
2. Description of the Prior Art
Molded case circuit breakers and interrupters are well known in the art as exemplified by U.S. Pat. No. 4,503,408 issued Mar. 5, 1985, to Mrenna et al., and U.S. Pat. No. 5,910,760 issued Jun. 8, 1999 to Malingowski, et al, each of which is assigned to the assignee of the present application and incorporated herein by reference.
A continuing industry objective with respect to many types of circuit interrupters is to be able to reduce the size and/or footprint of the interrupter housing while at the same time providing the same or improved performance capabilities. A major advantage of creating such a xe2x80x9csmaller packagexe2x80x9d is that it provides increased flexibility in installation. However, a consequence of this objective is that the internal space constraints of such interrupters have become much more limiting, posing certain design obstacles that need to be overcome.
Circuit interrupters advantageously provide for automatic circuit interruption (opening of the contacts) when an overcurrent condition is determined to exist. One way of determining whether or not an overcurrent condition exists is to provide a trip mechanism with a rotatable trip bar assembly and a bimetal through which current flows. The bimetal reacts to overcurrent conditions by heating up and bending towards the trip bar assembly. Above a predetermined current level (overcurrent conditions), the bimetal bends far enough so as to cause a rotation of the trip bar assembly which sets in motion a tripping operation.
It is desirable to be able to adjust the predetermined current level that causes the above-described thermal tripping operation. In the prior art, such adjustment could be made by changing the size and/or shape of the bimetal. In addition, adjustment could be made by selectively screwing a screw through an opening in a bottom portion of the bimetal such that it protrudes to a certain extent towards the trip bar assembly. The screw is positioned to contact the trip bar assembly (and cause rotation thereof) when the bimetal bends, and the variability of the extent of its protrusion towards the trip bar assembly selectively increases or reduces the amount of deflection that is necessary to cause a thermal tripping operation.
Although the above-described thermal trip adjustability is effective, it unfortunately requires that a circuit interrupter be opened so as to provide access to internal portions thereof. This inconvenience effectively causes the adjustment to be limited to factory implemention rather than by the end user.
Because of this drawback, trip mechanisms were subsequently developed in the prior art which enabled adjustment of the thermal tripping operation without requiring the opening of a circuit interrupter. These prior art trip mechanisms include a trip bar assembly that can slide longitudinally within the housing by means of an externally controlled mechanism. The trip bar assembly includes a thermal trip member having contact portions which protrude, to differing extents, towards the bimetal. As the trip bar assembly is caused to slide, different contact portions of the thermal trip member are positioned to make contact with a deflected bimetal, thus increasing or decreasing the amount of deflection that is necessary to cause a thermal tripping operation.
Unfortunately, enabling the entire trip bar assembly to slide longitudinally within the housing can be very problematic. First, enabling the entire trip bar assembly to slide requires more room in the circuit interrupter""s housing, which is contrary to the continuing industry objective mentioned above of creating a xe2x80x9csmaller package.xe2x80x9d Second, because the trip bar assembly of a circuit interrupter typically includes members which must be properly positioned in order to interact with the operating mechanism of the circuit interrupter, and members which must be properly positioned in order to be contacted by forces generated by other tripping operations, these members must be designed to account for the sliding of the trip bar assembly, which can be very difficult to accomplish.
In view of the above, it would be advantageous if a circuit interrupter trip mechanism existed that could provide for externally-controlled adjustment of a thermal tripping operation which did not require the entire trip bar assembly to slide longitudinally within the housing.
The present invention provides a circuit interrupter that meets all of the above-identified needs.
In accordance with the present invention, a circuit interrupter is provided which includes a housing, separable main contacts within the housing, and an operating mechanism within the housing and interconnected with the separable main contacts. A trip mechanism is disposed within the housing that includes a trip bar assembly rotatable about an axis and that, when rotated, generates a tripping operation causing the operating mechanism to open the contacts. The trip bar assembly includes a trip member translatable along the axis. The trip mechanism includes a tripping actuator movable along a predetermined path of travel as a function of electrical current. The tripping actuator contacts a contact area of the trip member at a predetermined location along the predetermined path of travel of the tripping actuator and causes the trip bar assembly to rotate and generate the tripping operation upon a predetermined current threshold. When the trip member is translated along the axis, the contact area is contacted by the tripping actuator at a different location along the predetermined path of travel of the tripping actuator whereby the predetermined current threshold is changed.
This and other objects and advantages of the present invention will become apparent from a reading of the following description of the preferred embodiment taken in connection with the attached drawings.